Weather type classifications (WTC) are widely used in meteorological applications and climate research. Currently, operational classifications for the Alpine region are subjective and manual, laborious and likely inhomogeneous in time. This project aimed at establishing a new objective weather type classification for the Alpine region that is suitable for ongoing operational and new applications of WTCs. The project was structured into three parts: In PART A candidate classification schemes were assessed for their suitability in the Alpine region. In PART B a new scheme for precipitation mapping was developed, which exploits information about the relationship between weather types and precipitation. PART C was originally aiming at the reconstruction of the objective WTCs back to the late 19th century. Due to withdrawal of one of the project partners this part could not be realized as planned. Instead, PART C was dedicated to the operational implementation of the new WTCs at MeteoSwiss. PART A: A new method has been developed for assessing the ability of WTCs to resolve surface climate variables. A skill measure from meteorological forecast verification (the Brier Skill Score) has been adopted for this purpose and was applied to compare all COST 733 WTCs with respect to their resolution of precipitation in the Alps and in Norway. The results point to a small number of classification schemes that represent precipitation particularly well. The skill of these new classifications was larger than that of classifications currently distributed by MeteoSwiss. PART B: A statistical method (reduced-space optimal interpolation) has been implemented and tested for mapping daily precipitation in the Alps. The method has been shown to be suitable for mapping in near real-time situations. A stratification of the mapping with respect to the prevailing weather type was shown to yield moderately better interpolation results, yet this strongly depends on the weather type. PART C: The analyses of Part A have been extended to identify particularly valuable classification techniques for Switzerland. Several of them have been implemented to produce regular and automatically updated weather type information. They provide new opportunities for understanding the dynamical causes of past climate variations, for processing of forecasts from numerical weather prediction models, for developing regional climate change scenarios, and for many other applications. The new WTCs for Switzerland are made available to users by MeteoSwiss via its official data distribution. They are documented in a user-oriented web page on
http://www.meteoswiss.ch, in a detailed technical report and in an illustrative plate of the Hydrological Atlas of Switzerland. The project also resulted in two lead-author and several co-authered peer-reviewed publications.
